Creep drive control device for driving vehicle at creep speed

ABSTRACT

A creep drive control device according to the invention sets a target creep vehicle speed when a driver has neither one of an acceleration intention or a stop maintenance intention. An engine output is increased (or decreased) by a vehicle speed increase processing (or a vehicle speed decrease processing), or a braking force is decreased (or increased), and an actual vehicle speed is controlled so as to be equal to the target creep vehicle speed or a value in the proximity thereof. The target creep vehicle speed, and respective engine output and braking force increase amounts and decrease amounts are corrected and set in accordance with driving conditions, road surface conditions and driver operations.

INCORPORATION BY REFERENCE

[0001] The disclosure of Japanese Patent Application No. 2002-250997filed on Aug. 29, 2002 including the specification, drawings andabstract is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to a creep drive control device forcausing a vehicle to drive at a constant creep speed. This creep drivecontrol device can be preferably utilized, for example, for starting ona sloping road.

RELATED ART OF THE INVENTION

[0003] Conventionally, vehicle starting has been made easier to executeby causing the vehicle to drive at a low speed that is substantiallyequivalent to a creep speed. However, conventional art does notfacilitate easy vehicle starting on upward or downward sloping roads.

[0004] Meanwhile, art (e.g., Japanese Patent Application Laid-OpenPublication 06-264783) has been disclosed that inhibits a vehicle fromslipping backwards on an upward sloping road by making it difficult forthe vehicle to go backwards (Japanese Patent Application Laid-OpenPublication 06-264783). This is achieved by controlling drive torquesuch that torque of creep speed drive becomes slightly larger thantorque of driving resistance during starting.

[0005] However, the object of this conventional art is to inhibit avehicle from slipping backward on an upward sloping road. Accordingly,this art does not cause a vehicle to drive at a desired low speed, orexecute driving control on a downward sloping road.

SUMMARY OF THE INVENTION

[0006] It is therefore an object of the invention to provide a creepdrive control device that causes a vehicle to starting easily at a lowspeed that is substantially equivalent to a creep speed, on an upward ordownward sloping road.

[0007] A creep drive control device according to the present inventionexecutes control such that, when the driver does not have an intentionto accelerate the vehicle, or an intention to stop a vehicle andmaintain a stopped state of the vehicle, a vehicle speed becomes a valuewithin a fixed range, as a result of adjustment of a braking force thatis applied to the vehicle, or/and adjustment of a driving force of thevehicle.

[0008] According to this creep drive control device, when the driverdoes not have the intention to accelerate the vehicle or the intentionto stop and maintain a stopped state of the vehicle, the braking forceis increased or decreased, or/and the driving force is increased ordecreased in order to make the vehicle speed become equal to the valuewithin the fixed range. Accordingly, regardless of the gradient of theroad which the vehicle is driving on, namely, regardless of whether theroad slopes upward or downward, it is possible to drive the vehicle at aspeed that is controlled to be within the fixed range.

[0009] Therefore, if this fixed speed is set, for example, to be a lowspeed that is substantially equivalent to a creep speed of a creepphenomenon generated by a torque converter of a transmission, when thedriver intends to accelerate during starting of the vehicle, it ispossible to easily execute starting of the vehicle from the creep speedwithout being constrained by the gradient of the road surface. Moreover,when the driver intends to stop the vehicle and maintain the stoppedstate, it is possible to smoothly stop the vehicle from the creep speedwithout being constrained by the gradient of the road surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Other objects, features and advantages of the present inventionwill be understood more fully from the following detailed descriptionmade with reference to the accompanying drawings. In the drawings:

[0011]FIG. 1 shows the entire structure of a creep drive control deviceof a first embodiment according to the present invention;

[0012]FIG. 2 shows the entire structure of a hydraulic brake device ofthe first embodiment;

[0013]FIG. 3 is a main flow chart showing a procedure of a creep drivecontrol device of the first embodiment and a second embodiment accordingto the present invention;

[0014]FIG. 4 is a flow chart showing a procedure of an accelerationintention determination of the first embodiment;

[0015]FIG. 5 is a flow chart showing a procedure of a stop continuationintention determination of the first embodiment;

[0016]FIG. 6 is a flow chart showing a procedure of a startingassistance control of the first embodiment;

[0017]FIG. 7 is a flow chart showing a procedure for setting a targetcreep vehicle speed of the first embodiment;

[0018]FIG. 8A to 8F are line diagrams that indicate respectivecharacteristics of correction coefficients K1 to K6 for setting of thetarget creep vehicle speed;

[0019]FIG. 9 is a diagram that shows input-output characteristics of avehicle speed limiting processing;

[0020]FIG. 10 is a flow chart showing a procedure of a vehicle speeddeceleration processing of the first embodiment;

[0021]FIG. 11A to 11I are line diagrams that indicate characteristics ofcorrection coefficients KEd1 and KEd2 of an engine decrease amount,correction coefficients KDT1 and KDT2 of a brake control initiationdelay time; and correction coefficients KBi1 to KBi5 of a brake controlincrease amount;

[0022]FIG. 12 is a flow chart showing a procedure for a vehicle speedacceleration processing of the first embodiment;

[0023]FIG. 13A to 13B are line diagrams that indicate characteristics ofcorrection coefficients KBd1 and KBd2 of a brake decrease amount duringa vehicle speed acceleration processing;

[0024]FIG. 14A to 14J are line diagrams that indicate characteristics ofcorrection coefficients KBd1 and KBd2 of a brake decrease amount,correction coefficients KEil and KEi5 of an engine control increaseamount, and correction coefficients R1 to R5 of an engine output emittervalue during a vehicle speed acceleration processing;

[0025]FIG. 15 is a control flow chart of a bridge control of the firstembodiment;

[0026]FIG. 16A to 16D are line diagrams that indicate characteristics ofcorrection coefficients M1 and M2 of a brake bridge control changeamount, and correction coefficients M3 and M4 of an engine bridgecontrol change amount;

[0027]FIG. 17 is a flow chart showing a procedure executed during brakeadjustment in the first embodiment;

[0028]FIG. 18 is a flow chart showing a procedure for a motor-drivenparking brake (PKB) output of the first and second embodiments;

[0029]FIG. 19 is a flow chart showing a procedure executed during brakeadjustment in the second embodiment;

[0030]FIG. 20 is a flow chart showing a procedure for a creep drivecontrol device of a third embodiment according to the present invention;

[0031]FIG. 21 is a flow chart showing a procedure executed during brakeadjustment in the third embodiment;

[0032]FIG. 22 is a section of a flow chart showing a procedure for amotor-driven PKB output of the third embodiment;

[0033]FIG. 23 is another section of the flow chart showing the procedurefor the motor-driven PKB output of the third embodiment;

[0034]FIG. 24 is a line diagram showing a relationship of a brakingforce requirement value of the motor-driven PKB and a wire stroke.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The present invention will be described further with reference tovarious embodiments in the drawings.

[0036] (First Embodiment)

[0037] A creep drive control device of a first embodiment according tothe invention will be described with reference to the drawings. FIG. 1shows the entire structure of the creep drive control device of thefirst embodiment, in which a front right wheel, front left wheel, rearright wheel and rear left wheel of a vehicle VL are respectivelydesignated as 4FR, 4FL, 4RR, and 4RL.

[0038] The vehicle VL shown in FIG. 1 is a front-wheel drive vehicle inwhich the forward wheels 4FR and 4FL are driven via axles 91R and 91L byan engine 80 and an automatic transmission (hereinafter referred to as“AT”) 90.

[0039] The creep drive control device is mounted in the vehicle VL. Thecreep drive control device is provided with a brake control electroniccontrol unit (hereinafter referred to as “ECU”) 1; a hydraulic brakedevice 2 as a first brake unit; a motor-driven parking brake(hereinafter referred to as “motor-driven PKB”) 3 as a second brakeunit; wheels 4FR and 4RL and wheels 4FL and 4RR that are diagonallyconnected to the hydraulic brake device 2 by a first brake circuit 21and a second brake circuit 22, respectively; brake wires 31L and 31Rthat connect respective brake calipers (not shown) of each of rearwheels 4RL and 4RR to the motor-driven PKB 3. Moreover, the creep drivecontrol device is also provided with vehicle wheel speed sensors 5FR,5FL, 5RR and 5RL that detect a rotational speed of each wheel; anon-board LAN bus 6 that transmits input and output signals of variouselectronic instruments; a sensor cluster 50 formed from a variety ofsensors connected to the on-board LAN bus 6; a starting assistancecontrol ECU 7; an engine control ECU 8; and an automatic transmissionECU (hereinafter referred to as “AT-ECU”) 9.

[0040] The brake control ECU 1 corresponds to a braking force controlunit of the invention, and is formed from a computer. The brake controlECU 1 calculates brake control amounts used in anti-lock brake system(ABS) control, vehicle stability control (VSC), and traction control(TCS), and the like, based on a vehicle wheel rotation signals ofrespective wheels 4FR, 4FL, 4RL and 4RR from the vehicle wheel speedsensors 5FR, 5FL, 5RL and 5RR, and each type of sensor signal input viathe on-board LAN bus 6 from the sensor cluster 50.

[0041] The brake control ECU 1 sends information including a vehiclespeed signal, a master cylinder pressure of the hydraulic brake device 2and a brake pedal operation amount to the starting assistance controlECU 7, described later. The brake control ECU 1 receives the brakecontrol amounts calculated by the starting assistance control ECU 7based on this information, and then determines respective brakeactuation signals (a first brake actuation signal and a second brakeactuation signal) based on these brake control amounts. These signalsare then output to the hydraulic brake device 2 and the motor-driven PKB3, and braking force is applied to each of the wheels 4FR, 4FL, 4RL and4RR.

[0042] In addition, the brake control ECU 1 calculates a surfacefriction coefficient (road surface μ) using a known method based on aslip ratio obtained from a difference between the calculated vehiclewheel speed and a vehicle speed (a vehicle-body speed).

[0043] Moreover, according to the invention, the brake control amountindicates a required control amount for obtaining a required brakingforce or a required deceleration. Moreover, within this specification,the term “brake pressure” corresponds to a wheel cylinder pressure(hereinafter referred to as “W/C pressure”) that generates “brakingforce”, and is therefore equivalent to “braking force”. For example, atarget deceleration that corresponds with a target braking force isconverted to a brake pressure based upon the equation of deceleration 1G=10 MPa, (where, G is a gravitational acceleration and Pa is a Pascal(unit of pressure)). Note that, the above equation is defined since: Pais a Pascal indicating a unit of pressure and 1 MPa of the W/C pressureis equivalent to 0.1 G (gravitational acceleration) of deceleration.

[0044] The hydraulic brake device 2 is configured as shown in FIG. 2.When the vehicle driver depresses a brake pedal (not shown), a mastercylinder (hereinafter referred to as “M/C”) 10 produces an M/C pressurecorresponding to a depression force. The M/C pressure is transmitted toW/Cs 41FR, 41RL, 41FL, and 41RR provided in the respective wheels 4FR,4RL, 4FL and 4RR via the corresponding first brake circuit 21 and thesecond brake circuit 22, in order to generate a first braking force.Next, the first brake circuit 21 will be described with particularemphasis on the brake circuit related to the front right wheel 4FR.However, the same description applies to the other wheels 4FL, 4RR and4RL of the first brake circuit 21 and the second brake circuit 22.

[0045] The first brake circuit 11 is provided with pressure increasecontrol valves 14 a and 14 b that adjust pressure increasing andpressure maintenance for the respective W/Cs 41FR and 41RL in an antiskid control (hereinafter referred to as “ABS control”) for the frontright wheel 4FR and the rear left wheel 4RL, respectively. Further, thepressure increase control valves 14 a and 14 b are arranged in parallelwith check valves 141 a and 141 b, respectively, in order to allow fluidflow to be directed toward the M/C 10 if the W/C pressure is excessiveduring the closure of each of the pressure increase control valves 14 aand 14 b. Pressure decrease control valves 15 a and 15 b are provided ina pressure decrease line 12 extending from a point between the pressureincrease control valves 14 a and 14 b and the W/Cs 41FR and 41RL. Thesepressure decrease control valves 15 a and 15 b adjust pressure decreaseand pressure maintenance of the W/Cs 41FR and 41RL in the ABS control.

[0046] The pressure decrease line 12 is connected to a reservoir 16. Thereservoir 16 stores brake fluid and has a check valve for adjusting abrake fluid pressure therein. This brake fluid is sucked up by a pump 17driven by a motor 20, and then discharged into the first brake circuit21. The discharge destination is a point between the pressure increasecontrol valves 14 a and 14 b and a master cut valve (hereinafterreferred to as “SM valve”) 18. The motor 20 also drives a pump 27 in thesecond brake circuit 22. Further, a check valve 171 is provided in theoutlet of the pump 17.

[0047] The SM valve 18 is disposed between the M/C 10 and the pressureincrease control valves 14 a and 14 b. The SM valve 18 is a two-positionvalve that is in a opened state when non-energized, and is in a closedstate when energized, due to a check valve positioned in the directionshown in FIG. 2. In the closed state, the pressure in the W/Cs 41FR and41RL is cancelled when it is higher than the pressure in the M/C 10 bythe amount of a component of pressure caused by the spring of the checkvalve. Accordingly, a pressure release structure is realized. The SMvalve 18 is arranged in parallel with a check valve 181, and as a resultonly flow from the M/C 10 toward the W/Cs 41FR and 41RL is permitted.

[0048] A suction line 13 establishes a connection between the reservoir16 and a point between the M/C 10 and the SM valve 18.

[0049] An fluid pressure sensor 30 that detects pressure generated inthe M/C 10 is provided between the M/C 10 and the SM valve 18 in thefirst brake circuit 21. The pressure detected by the fluid pressuresensor 30 is a pressure generated in a secondary chamber (not shown) ofthe M/C 10. It should be noted that the same pressure is produced in aprimary chamber thereof, which is connected to the second brake circuit22. Hence, the fluid pressure sensor 30 effectively detects the M/Cpressure. Further, fluid pressure sensors 19 a and 19 b that detect eachW/C pressure are respectively provided between the pressure increasecontrol valve 14 a and the W/C 41FR, and between the pressure increasecontrol valve 14 b and the W/C 41RL. The output signals from these fluidpressure sensors 30, 19 a and 19 b are input to the brake control ECU 1.

[0050] Each of the above pressure increase control valves 14 a and 14 b,and the pressure decrease control valves 15 a and 15 b is a two-positionvalve, which is in the valve position illustrated in FIG. 2 whennon-energized (i.e., OFF), such as when the brake pedal is not applied,or during normal braking operation, or the like. In other words, whennon-energized, the pressure increase control valves 14 a and 14 b are inthe opened state and the pressure decrease control valves 15 a and 15 bare in the closed (cut-off) state. Further, during normal non-energizedperiods, the SM valve 18 is in the valve position illustrated in FIG. 2,namely, the opened state. Each of the above control valves is operatedby an actuating signal supplied by the brake control ECU 1. Moreover,the motor 20 driving the pumps 17 and 27 is operated by a brakeactuating signal supplied by the brake control ECU 1.

[0051] It should be noted that the individual actuating signals suppliedfrom the brake control ECU 1 to the hydraulic brake device 2 correspondin aggregate to a first actuating signal. Further, placing the hydraulicbrake device 2 into a control pause (or control prohibited) stateindicates placing the first actuating signal in an inactive state,namely to zero (the non-actuating state). Specifically, in this controlpause state, none of the pressure increase control valves 14 a and 14 b,the pressure decrease control valves 15 a and 15 b and the SM valve 18(as well as pressure increase control valves 24 a and 24 b, pressuredecrease control valves 25 a and 25 b and an SM valve 28 in thesecondary brake circuit 22) are energized, and the driving current ofthe motor 20 becomes zero. Accordingly, when the first actuating signalbecomes inactive, the W/C pressure for each wheel 4FR, 4FL, 4RR, and 4RLis decreased to zero and therefore the first braking force becomes zero.

[0052] Next, a description will be given of the braking operationcarried out on the basis of each of the command values for pressureincreasing, pressure maintenance and pressure decrease, which correspondto the first actuating signal supplied from the brake control ECU 1.This braking operation is carried out regardless of the automaticbraking operation of the above hydraulic brake device 2, namely,regardless of whether the brake pedal is applied. Note that theoperation based on brake pedal application by the driver which is thenormal operation, and the operation in the ABS control are well known,and thus a description will be omitted here.

[0053] In the pressure increase processing in the automatic brakingcontrol, the SM valve 18 is switched to ON (the cut-off position) andfurther the pressure decrease control valve 15 a is switched to OFF (thecut-off position). Then, the pump 17 is driven to draw up brake fluidand then discharge it via the reservoir 16. While the pump 17 generatesthe discharge pressure, a comparison with the value detected by thefluid pressure sensor 19 a is performed, and at the same time thepressure increase control valve 14 a undergoes ON/OFF duty ratiocontrol. This causes a increase of the W/C pressure at a predeterminedchange gradient or to a preset target pressure. At this point, the brakefluid is refilled as required from the M/C 10 to the inlet of the pump17, through the suction line 13 and the reservoir 16.

[0054] In the pressure decrease processing in the automatic brakingcontrol, the SM valve 18 is switched to ON (the cut-off position) andalso the pressure increase control valve 14 a is switched to ON (thecut-off position). Then, the pump 17 is driven to draw up brake fluidand then discharge it via the reservoir 16. While the pump 17 generatesthe discharge pressure, a comparison with the value detected by thefluid pressure sensor 19 a is performed, and at the same time thepressure decrease control valve 15 a by ON/OFF duty ratio control.Thereby, brake fluid is drawn from the W/C 41FR to decrease the W/Cpressure at a predetermined variation gradient or to a preset targetpressure.

[0055] At this point, due to both the pressure increase control valve 14a and the SM valve 18 being in the cut-off position, the dischargepressure of the pump 17 rises. When the rising pressure exceeds theelastic force of the spring in the check valve of the SM valve 18, thepressure is cancelled and pressure decrease takes place.

[0056] In the pressure-maintenance processing in the automatic brakingcontrol, the SM valve 18 is switched to ON (the cut-off position), andboth the pressure increase control valve 14 a and the pressure decreasecontrol valve 15 b are switched to the cut-off positions. Accordingly,the W/C pressure is maintained.

[0057] Next, the motor-operated PKB 3 serving as the second brake unitwill be described.

[0058] When the vehicle VL is in a stopped state, the motor-operated PKB3 maintains the stopped state. Specifically, the motor-operated PKB 3 isoperated according to the second actuating signal from the brake controlECU 1. In the motor-operated PKB 3, an actuator including a motor and agear mechanism (none of these elements are shown) drives each of thebrake wires 31R and 31L, in order to press the brake caliper and afriction material in each of the wheels 4RR and 4RL against thecorresponding brake disc (not shown) so as to generate a braking force.

[0059] The motor of the motor-operated PKB 3 is duty controlled based onthe control of the second actuating signal so as to rotate in the normaldirection (increase in braking force), or in the opposite direction(decrease in braking force), thereby allowing control of the magnitudeof a second braking force.

[0060] At this point, the braking force is generated in accordance withthe duty ratio. When this braking force reaches the target brakingforce, the motor of the motor-operated PKB 3 is locked. When locking ofthe motor is detected, the driving current for the motor is interrupted,namely the second actuating signal becomes inactive, so as to bring themotor-operated PKB 3 into the control pause (control prohibited) state.When the motor-operated PKB 3 is in the control pause state, the gearmechanism does not operate. Accordingly, the braking force ismaintained, and a locked state of the wheels 4RR and 4RL is maintained.

[0061] Such operation of the motor-operated PKB 3 is executed inaccordance with the second actuating signal supplied from the brakecontrol ECU 1 during automatic brake control. Alternatively, themotor-operated PKB 3 may be operated such that when the driver switchesa parking brake switch (not shown) to ON or OFF, the brake control ECU 1outputs the second actuating signal for the motor-operated PKB 3 inresponse to this signal.

[0062] As illustrated in FIG. 2, the wheel speed sensors 5 includes thewheel speed sensors 5FR, 5FL, 5RR, and 5RL for detecting the rotationalspeed of respective wheels 4FR, 4FL, 4RR and 4RL. Output signals fromthe sensors 5FR, 5FL, 5RR and 5RL are input directly to the brakecontrol ECU 1.

[0063] It should be noted that a semiconductor speed sensor using a Hallelement is employed for each of the wheel speed sensors 5FR, 5FL, 5RRand 5RL. Hence, even when travelling at low speeds, a pulse signal isobtained that reliably indicates the vehicle wheel rotational speed androtation direction. This makes it possible to detect a precise vehiclewheel speed even when the vehicle is caused to move from the stoppedstate to a moving state.

[0064] The sensor cluster 50 is provided with a brake operation amountsensor 51, an accelerator operation amount sensor 52, a shift positionsensor 53, a vehicle-surround monitoring sensor 54, a gradient sensor53, and a vehicle stop maintenance start switch 56.

[0065] The brake operation amount sensor 51 detects an operation amountof the brake pedal. The accelerator pedal operation amount sensor 52detects an operation amount of an accelerator pedal (not shown), namely,an accelerator opening.

[0066] The shift position sensor 53 detects shift position informationin accordance with a shift position state. Here, the shift positionstate refers to the shift position of the AT 90, such as D (drive), 2(second), L (low), R (reverse), N (neutral) and P (parking). These shiftpositions are selected by the operation of a gearshift lever by thedriver. If the shift position sensor 53 detects the D range (or the 2range or the L range) it can be determined that the driver's intendedmovement direction is forward, whereas, if the R range is detected itcan be determined that the driver's intended movement direction isbackward.

[0067] The vehicle-surround monitoring sensor 54 is provided at a frontportion or a back portion of the vehicle VL, for example, in a bumper,and uses a laser radar to measure a distance x from the vehicle VL to anobstacle that exists in front of or behind the vehicle VL. The gradientsensor 55 detects an angle of the vehicle body with respect to ahorizontal plane, namely, an upward gradient or a downward gradient. Thevehicle stop maintenance start switch 56 is operated by the driver andgenerates a signal for starting vehicle stop maintenance control.

[0068] Further, the sensor output of the shift position sensor 53 isdirectly input to the AT-ECU 9. The other ECUs may obtain the shiftposition information from the AT-ECU 9 via the on-board LAN bus 6.Moreover, it is possible for the upward gradient and the downwardgradient to be estimated by calculation by the brake control ECU 1 usinga known method (e.g., that disclosed in Japanese Patent Laid-OpenPublication No. 06-264783), instead of by using the gradient sensor 55.

[0069] Known devices may be used for each of the aforementioned sensors,and thus a detailed explanation will be omitted here.

[0070] The starting assistance control ECU 7 is configured from acomputer and receives the shift position information from the shiftposition sensor 53, actual gear position information from the AT-ECU 9,and so on. The starting assistance control ECU 7 executes processing inaccordance with a procedure shown in a flow chart that will be describedlater. Accordingly, the starting assistance control ECU 7 calculates arequired engine control amount and a required brake control amount anddetermines a downshift requirement for causing the vehicle VL to drivein a creep driving mode, and outputs the amounts and the requirement tothe engine control ECU 8, the brake control ECU 1, and the AT-ECU 9,respectively. Thus, the starting assistance control ECU 7 corresponds toa drive acceleration intention unit, a stop maintenance intention unit,a target creep setting unit, a vehicle speed acceleration unit, avehicle speed deceleration unit, and a starting assistance control unitaccording to the invention.

[0071] The engine control ECU 8 is configured from a computer. Theengine control ECU 8 executes engine output control by adjustment of anengine fuel injection amount and an injection time, based upon theengine control amount calculated in accordance with the depressionamount of the accelerator pedal caused by an ordinary driver, namely,the accelerator opening, and also upon the engine control amountcalculated by the starting assistance control ECU 7. Here, the enginecontrol amount refers to a required throttle opening. The engine controlECU 8 corresponds to an engine output control unit according to theinvention.

[0072] The AT-ECU 9 is configured from a computer. As with normaltransmission control, the AT-ECU 9 determines a shift gear ratio inaccordance with a predetermined shift pattern map that is based on theshift position information from the shift position sensor 53, theaccelerator opening detected by the accelerator operation amount sensor52, and the calculated speed, and then executes shifting. Moreover,according to this embodiment, when the downshift requirement is outputfrom the starting assistance control ECU 7, downshift is executed thatinterrupts the automatic transmission control. Moreover, the AT-ECU 9transmits the actual gear position information to the startingassistance control ECU 7. It should be noted that the actual gearposition information and the shift position information from the shiftposition sensor 53 are essential for determining whether to downshift.

[0073] Next, an operation procedure of the creep drive control deviceaccording to the first embodiment will be explained based on the mainflow chart shown in FIG. 3.

[0074] This main flow chart is executed by the starting assistancecontrol ECU 7 and the brake control ECU 1. The starting assistancecontrol ECU 7 and the brake control ECU 1 operate cooperatively in anintegrated form so as to execute each processing. It goes without sayingthat the processing in the flow chart can be executed with the startingassistance control ECU 7 and the brake control ECU 1 adopting completelyseparate forms, or alternatively, with the starting assistance controlECU 7 integrated with an ECU other than the brake control ECU 1.

[0075] Each processing shown in the flow chart is initiated when theignition is turned on, and is repeatedly executed with a predeterminedcontrol cycle (for example, 5 to 10 ms).

[0076] At 100, an initial check is executed. At this point, the brakecontrol ECU 1 executes an operation check of each actuator of thehydraulic brake device 2 and the motor-driven PKB 3.

[0077] More specifically, a disconnection check is executed by actuallyenergizing each electromagnetic valve of the hydraulic brake device 2and executing a check of the terminal voltages of each electromagneticvalve of the brake control ECU 1. Moreover, a failure locationidentification is executed by determining whether there are anyhydraulic pressure abnormalities based on the detection values of thefluid pressure sensors 30, 19 a and 19 b, and fluid pressure sensors 29a and 29 b.

[0078] Moreover, failure location identification is executed bydetermining whether a detected current is normal when the motor-drivenPKB 3 is actually energized, and whether the motor of the motor-drivenPKB 3 rotates normally, and the like. In the case that a failure isdetected, the system is configured such that, following failurediagnosis in the motor-driven PKB3, control is prohibited, an alternatecontrol is switched to, and a warning lamp is lit. Thus, it is possibleto prevent a fatal failure from occurring such as abnormal operation ofany portion of the brake device, and the like, from occurring. Alongwith this, the starting assistance control ECU 7 can suspend startingassistance control and switch to an alternative control, based on therespective failure diagnosis results of the brake control ECU 1, theengine control ECU 8, and the AT-ECU 9.

[0079] At 110, an input processing is executed in which detection datafrom each sensor are input.

[0080] At 120 and 130, respectively, the starting assistance control ECU7 determines whether the driver has an acceleration intention andwhether the driver has a stop maintenance intention (throughout thisspecification the term “stop maintenance intention” refers to theintention to stop a vehicle and maintain the stopped state of thevehicle thus achieved, as well as an intention to maintain a stoppedstate of the vehicle), based on a flow chart (shown in FIGS. 4 and 5),to be described later. When it is determined that the driver has theacceleration intention, or when it is determined that the driver has thestop maintenance intention, there is no necessity to execute thestarting assistance control. Accordingly, it is determined whethereither of these cases applies in the given situation.

[0081] At 140, the brake control ECU 1 calculates the brake controlamount and the engine control amount that accord with the braking forcerequirement for the ABS control, the VSC control and the TCS control.

[0082] At 150, the starting assistance control is executed based on aflow chart described hereinafter (refer to FIG. 6). This processing isexecuted by the starting assistance control ECU 7 and includes executinga vehicle speed acceleration control and/or a vehicle speed decelerationcontrol such that, for example, an actual vehicle speed becomes equal toa target creep vehicle speed. In other words, the engine control amountand the brake control amount are calculated so as to control the engineoutput and the braking force in order to execute these controls.Moreover, when it is determined that the driver's intention has switchedto either the acceleration intention or the stop maintenance intentionat 120 and 130, the vehicle acceleration control and the vehicledeceleration control are terminated. Then, bridge control is executedsuch that the engine control amount and the brake control amountconverge on and eventually equal values that accord with an operationamount of the driver.

[0083] Processing at 160 is executed by the brake control ECU 1. At 160,a brake control adjustment control is executed in which the brakecontrol amount corresponding to the braking force requirement calculatedat 140 is compared to the brake control amount corresponding to thebraking force requirement calculated at 150, and a brake control amountis selected that corresponds to the largest of these braking forcerequirements. Then, target braking forces for the hydraulic brake device2 and the motor-driven PKB 3, respectively, are determined in accordancewith the braking force requirement selected in the brake controladjustment.

[0084] At 170, a fail safe check when the ignition is ON is executed.Namely, a normal diagnosis test of the status of the brake control ECU1, the hydraulic brake device 2, the motor-driven PKB 3, the startingassistance control ECU 7, the engine control ECU 8, the AT-ECU 9, andthe various other sensors, is executed. In the case that a failure isdetected, predetermined processing is executed so that the vehicle VLcan be driven safely or stopped, even if the portion detected to have afailure is not functioning.

[0085] At 180, the brake control ECU 1 controls the first actuatingsignal such that the first braking force of the hydraulic brake device 2that is generated in accordance with the first actuating signal becomesequal to the target braking force set at 160.

[0086] At 190, the brake control ECU 1 controls the second actuatingsignal such that the second braking force of the motor-driven PKB 3 thatis generated in accordance with the second actuating signal becomesequal to the target braking force set at 160.

[0087] At 195 the engine control amount for the VSC control and the TCScontrol calculated at 140 by the brake control ECU 1, and the enginecontrol amount for the starting assistance control calculated at 150 bythe starting assistance control ECU 7 are transmitted to the enginecontrol ECU 8 from the brake control ECU 1. Based on these enginecontrol amounts, various types of engine control signal are output tothe engine control ECU 8.

[0088] Next, the flow of the acceleration intention determination ofaforementioned processing at 120 will be described with reference toFIG. 4.

[0089] At 202, it is checked whether any other automatic drive controlsare being executed. Such other automatic drive controls are, forexample, congestion adaptive cruise control of a congestion adaptivecruise control ECU (not shown); in this control, when the distancebetween the vehicle VL and a vehicle in front becomes equal to apredetermined value or less, braking force is automatically generated inorder to prevent a collision with the vehicle in front. In the check at200, it is determined that another automatic drive control is beingexecuted when a control, such as this congestion adaptive cruisecontrol, is being executed. When the result is YES, it is determinedthat the driver has the acceleration intention, and the routine proceedsto 210. When the result is NO, the routine proceeds to 202.

[0090] At 200, it is determined whether the vehicle speed is equal to apredetermined value or more, for example, whether the vehicle speed isequal to or more than 15 km/h, which is slightly faster than a referencecreep vehicle speed. If the result is YES, it is determined that thedriver has the acceleration intention. If the result is NO, the routineproceeds to 204.

[0091] At 204, it is determined if the shift position is a driveoperable position, namely, is one of the D, 2, L and R positions. If theresult is NO, namely, the shift position is P or N, it is determinedthat the driver does not have the acceleration intention and the routineproceeds to 208. If the result is YES, the routine proceeds to 206.

[0092] At 206, if an accelerator operation amount is equal to apredetermined value A or more, it is determined that the driver has theacceleration intention. If this is not the case, it is determined thatthe driver does not have the acceleration intention.

[0093] At this point, it is determined that the driver does not have theacceleration intention when no other automatic drive controls are beingexecuted, the vehicle speed is equal to 15 km/h or less, and the shiftposition is the P or N position. Alternatively, it may be determinedthat the driver does not have the acceleration intention when no otherautomatic drive controls are being executed, the vehicle speed is equalto 15 km/h or less, the shift position is one of the D, 2, L and Rpositions, and the accelerator operation amount is equal to thepredetermined amount A or less.

[0094] On the other hand, the stop maintenance determination ofprocessing at 130 shown in FIG. 3 is executed in accordance with theflow chart shown in FIG. 5.

[0095] First, at 250, it is determined whether the vehicle stopmaintenance start switch 56 is on. If the vehicle stop maintenance startswitch 56 has been switched to ON, it is determined that the driver hasthe stop maintenance intention at 260. If the vehicle stop maintenancestart switch 56 has not been switched to ON, the routine proceeds to252.

[0096] At 252 it is determined whether a vehicle stop maintenancecondition has been established. More particularly, for example, thecondition may be set as whether a stopped state (vehicle speed equalszero) has been maintained for 5 sec. or longer. If the result is YES, itis determined that the driver has the stop maintenance intention,whereas, if the result is NO, the routine proceeds to 254.

[0097] At 254, it is determined whether the shift position is a driveinoperable position, namely, the P or N positions. If the result is YES,it is determined that the driver has the stop maintenance intention. Ifthe result is NO, namely the shift position is one of the D, 2, L or Rpositions, the routine proceeds to 256.

[0098] At 256, it is determined whether a brake operation amount hasexceeded a predetermined value B. If the result is YES, it is determinedthat the driver has the stop maintenance intention. If the result is NO,it is determined that the driver does not have the stop maintenanceintention and the routine proceeds to 258.

[0099] If, up to this point, it has been determined that the driver doesnot have the stop maintenance intention, it is because the vehicle stopmaintenance switch 56 has not been switched to ON, the stop maintenancecondition (in this case, whether stop maintenance has been continued for5 sec. or longer) has not been satisfied, and the shift position is onethat makes drive inoperable, and the brake operation amount is equal tothe predetermined value B or less.

[0100] Next, the starting assistance control of processing at 160 shownin FIG. 3 will be explained with reference to the flow chart shown inFIG. 6.

[0101] At 300 it is checked whether the driver has the accelerationintention based on the determination result of processing at 120. If theresult of processing at 300 is YES, namely, if the driver has theacceleration intention, the routine proceeds to the bridge control ofprocessing at 314. If the result is NO, namely, if the driver does nothave the acceleration intention, the routine proceeds to 302.

[0102] At 302, it is checked whether the driver has the stop maintenanceintention based on the determination result from 130. If the result ofprocessing at 302 is YES, namely, the driver has the stop maintenanceintention, the routine proceeds to the bridge control at 314. If theresult is NO, namely, the driver does not have the stop maintenanceintention, the routine proceeds to 304.

[0103] At 304, a starting assistance control in-progress flag is setthat indicates that the starting assistance control is being executed.Along with this, a target creep vehicle speed α is set in accordancewith a procedure described hereinafter (refer to FIG. 7).

[0104] At 306, it is determined whether the actual vehicle speed isgreater than the target creep vehicle speed α. More accurately speaking,a dead zone β for stabilizing control is set, and it is determinedwhether the actual vehicle speed is larger than a second target vehiclespeed which is equal to α+β. If the result is YES, the routine proceedsto 310, and a vehicle speed deceleration processing shown in FIG. 10 isexecuted. If the result is NO, the routine proceeds to 308.

[0105] At 308, it is determined whether the actual vehicle speed islower than a first target vehicle speed that is α−β. If the result isYes, the routine proceeds to 312, and a vehicle speed accelerationprocessing shown in FIG. 12 is executed. If the result is NO, it isinferred that the vehicle speed is within a fixed range (α≦actualvehicle speed≦α+β), and the starting auxiliary control is terminated.

[0106] Next, the flow of the routine for setting the target creepvehicle speed α at 304 will be explained.

[0107] First, in processing from 400 to 410, the reference creep vehiclespeed that is pre-set is corrected in accordance with the drivingconditions, the road surface conditions and driver operations. In orderto do so, first, correction coefficients K1 to K6 for deriving thetarget creep vehicle speed α are calculated based on the map shown inFIGS. 8A to 8F.

[0108] Correction coefficient K1 is set so as to increase from 1 inaccordance with the magnitude of the accelerator opening caused by thedriver.

[0109] Correction coefficient K2 is set so as to decrease from 1 inaccordance with the magnitude of the brake operation amount of thedriver.

[0110] Correction coefficient K3 is set to a value that accords with thevehicle travel direction determined based on the vehicle speed signal;the value of correction coefficient K3 is set at 1, and is not correctedwhen the vehicle moves forward (i.e., the value remains at 1) andbecomes smaller than 1 when the vehicle moves backward.

[0111] Correction coefficient K4 is based upon sensor information of thegradient sensor 55, and is set so as to decrease from 1 in accordancewith increase in a gradient of an upward sloping gradient, and increasefrom 1 in accordance with decrease in a gradient of a downward gradient.

[0112] Correction coefficient K5 is set in accordance with the distancex that is detected by the vehicle-surround monitor sensor 54 between thevehicle VL and the obstacle that exists in the vehicle's traveldirection. Correction coefficient K5 is set so as to increase toward 1from a value smaller than 1 as the distance between the vehicle and theobstacle becomes larger.

[0113] Correction coefficient K6 is set in accordance with acontinuation time T that indicates how long a state has continued inwhich braking force is equal to a predetermined value or above.Correction coefficient K6 is set so as to increase from 1 as thecontinuation time T becomes longer.

[0114] At 412, the multiple of the above calculated correctioncoefficients K1 to K6 and the pre-set reference creep vehicle speed isset as the target creep vehicle speed α. Accordingly, the referencecreep vehicle speed is corrected upward or downward in accordance witheach correction coefficient K1 to K6, and the target creep vehicle speedα is derived.

[0115] At 414, a speed limiting processing for limiting the abovecalculated target creep vehicle speed α such that it is within apredetermined value range. In other words, as shown by the speedlimiting characteristics in FIG. 9, the target creep vehicle speed α islimited such that during creep driving the vehicle speed cannot becomeexcessive; for example, an upper limit value of 10 km/h may be set.

[0116] Further, in this speed limiting processing, the upper limit valueof the target creep vehicle speed a is set to become larger inaccordance with lengthening of the continuation time T of the state inwhich braking force is equal to or above the predetermined value,namely, the creep control continuation time T. FIG. 9 shows an exampleof determination of limit values of the target creep vehicle speed α.More particularly, when the continuation time T<t1, the target creepvehicle speed α is limited to α1 even if the calculated target creepvehicle speed α is above 1. When t1≦T≦t2, the target creep vehicle speedα is limited to α2 (>α1) even if the calculated target creep vehiclespeed α is above α2. Further, when t2<T≦t3, the target creep vehiclespeed α is limited to α3 (>α2) even if the calculated target creepvehicle speed α is above α3. Accordingly, the speed limiting processingmakes it possible, for example, to increase the target value anddecrease the braking force so as to inhibit generation of damageresulting from, for example, heat discharged by brake rotors due toapplying for a long period the braking force necessary to maintain thetarget creep vehicle speed α on a long downward slope.

[0117] As a result of the processing of the previously describedprocessing up to processing at 414, the corrected target creep vehiclespeed α is determined in accordance with the driving conditions, theroad surface conditions, and driving operations.

[0118] Next, in at 416, a speed deviation dV of the target creep vehiclespeed α and the actual vehicle speed Vs0 is calculated (dV=α−Vs0).Further, a gradient (a differential value) of this speed deviation dV isalso calculated (dV/dt). The speed deviation gradient is calculatedaccording to Equation (1) below:

dV/dt=(dV(t)−dV(t−1))/Δt  (1)

[0119] where, Δt is a control period (e.g., 5 ms); dV (t) is a speeddeviation of this calculation period; and dV (t−1) is a speed deviationof a prior calculation period.

[0120] At 418, it is determined whether the absolute value |dV| of thespeed deviation dV has exceeded a pre-set hysteresis value S. If thehysteresis value S has not been exceeded, the routine is terminatedsince it is assumed that even if the target creep vehicle speed α isset, there will be no sudden vehicle speed change. If the hysteresisvalue S has been exceeded, the routine proceeds to 420.

[0121] At 420, if the speed deviation is large, the target creep vehiclespeed α is changed to a value that is the sum of the actual vehiclespeed Vs0 and a predetermined value Z, rather than being set to thecalculated value of processing at 414. Following this, the routine isterminated. Here, the predetermined value Z, as shown by Equation (2),is a value calculated as the linear sum (X and Y are coefficients) ofthe speed deviation dV and the speed deviation gradient.

Z=X·dV+Y·dV/dt  (2)

[0122] Accordingly, when the speed deviation is large, the vehicle speedis gradually changed in each control cycle using the value that is thesum of the actual vehicle speed and the predetermined value Z to renewthe new target vehicle speed value. Accordingly, sudden changes in thevehicle speed are prevented.

[0123]FIG. 10 shows the flow of the vehicle speed decelerationprocessing executed at 310 (refer to FIG. 6). The portion of the brakecontrol ECU 1 that executes this vehicle speed deceleration processingflow corresponds to the vehicle speed deceleration unit according to theinvention.

[0124] At 500, it is determined whether engine control that is notdirectly related to accelerator operation is being executed, namely,whether engine control of the starting assistance control, or enginecontrol of the VSC control and TCS control is being executed. Thisdetermination is executed in order to make sure that, first, the vehiclespeed deceleration of engine control is given priority in execution;when this engine control is completed, downshifting and brake controlamount increase processing of the vehicle speed deceleration processingare executed. If engine control is being executed the routine proceedsto 502, whereas, if engine control is not being executed, the routineproceeds to 506.

[0125] At 502, an engine decrease amount TEd for decreasing engineoutput for each control period is calculated based on Equation (3) inwhich the linear sum of the absolute value |dV| of the speed deviationdV (dV =α−Vs0) and the speed deviation gradient |dV|/dt is correctedusing the road surface μ (road surface coefficient of friction) and thebrake operation amount.

TEd=KEd 1(μ)·KEd 2(brake)·(KEd 3 ·|dV|+KEd 4 |dV|/dt)  (3)

[0126] where, KEd1, as shown in FIG. 11(A), is a coefficient set todecrease from 1 in accordance with decrease of the road surface μ; inother words, the coefficient KEd1 is set such that, when the roadsurface μ is low, the engine decrease amount becomes smaller in order tominimize the impact on vehicle behavior caused by engine brake (e.g.,inclination of the vehicle body in the forward or backward directions):and KEd2, as shown in FIG. 11(B), is a coefficient that is set toincrease from 1 in accordance with increase of the brake operationamount; in other words, the coefficient KEd2 is set such that, when theoperation amount of the brake pedal is large, the engine decrease amountbecomes larger since it is necessary to rapidly cancel the enginecontrol. Further, KEd3 and KEd4 are pre-set proportionalitycoefficients.

[0127] At 504, the engine decrease amount TEd determined as describedabove is taken as an output decrease gradient, and a new engine controlamount ET is set which is a value equal to a prior period engine controlamount ET (t−1) minus the engine decrease amount TEd. Then, the routineis exited.

[0128] On the other hand, when it is determined at 500 that enginecontrol is not in-progress, at 506, it is determined whether downshiftfor decelerating the vehicle is possible based on the gear positioninformation. This gear position information indicates the transmissiongear actually selected by the AT 90 when the shift position is set tothe D position. The gear position of the AT 90 is normally selected fromone of a 1st speed to a 3rd speed even when the vehicle is moving at alow speed equivalent to a creep speed. Accordingly, if the gear positionis the 2nd speed or above, it is determined that downshift is possible,and a downshift requirement flag is set at 508. Based on this flaginformation, the downshift requirement is transmitted to the AT-ECU 9.

[0129] In the case that the gear position is the 1st speed, downshift isnot possible and thus the routine proceeds to 510.

[0130] At 510, a delay time DBT for initiating brake control once apredetermined time period has elapsed is assigned by deducting a valuethat is proportional to the absolute value |dV| of the speed deviationdV and the speed deviation gradient |dV|/dt from a reference valueDBT_(init). This is conducted because it is necessary to executedeceleration rapidly in the case that the speed deviation dV and thespeed deviation gradient are large. More specifically, the delay timeDBT is set based upon Equation (4) below:

DBT=DBT _(init) −KDT 1(μ)·KDT 2(Vso)·(KDT 3 ·|dV|+KDT 4 ·|dV|/dt)  (4)

[0131] where, KDT1, as shown in FIG. 11(C), is a coefficient set todecrease from 1 in accordance with decrease of the road surface μ; inother words, the coefficient KDT1 is set such that, when the roadsurface μ is low, the engine decrease amount based on the referencevalue DBT_(init) becomes smaller in order to inhibit the vehiclebehavior from becoming unstable due to braking: and KDT2, as shown inFIG. 11(D), is a coefficient that is set to increase from 1 inaccordance with increase of the vehicle speed; in other words, when thevehicle speed is high, it is desirable to decelerate in a rapid manner,and thus the coefficient KDT2 is set such that the engine decreaseamount based on the reference value DBT_(init) becomes larger. Further,KEd3 and KEd4 are pre-set proportionality coefficients.

[0132] Next, at 512, it is determined whether the delay time DBT haselapsed since it was determined that a state in which downshift isimpossible came into existence following a state in which downshift waspossible, based on the determination of processing at 506.Alternatively, at 512, it may be determined whether there has been anyhistory of downshift.

[0133] The downshift history is determined based on whether there is anyhistory of the downshift requirement flag being set. More particularly,as shown in FIG. 6, it is determined whether a downshift requirement hasbeen output following transition to vehicle speed deceleration controlfrom processing that had previously been selected that was different tothe vehicle speed deceleration processing (namely, when one of thevehicle speed acceleration processing (processing at S312), the bridgecontrol processing (processing at S314), and no specific processing wasselected).

[0134] If the determination result of processing at 512 is YES, theroutine proceeds to 514, whereas, if the determination result is NO, theroutine is exited.

[0135] At 514, a brake control increase amount TBi is derived, and alongwith this, a W/C pressure increase control flag is set that indicatesthat the W/C pressure has been increased by the automatic brake controlin order to generate braking force. The brake control increase amountTBi is set to become larger as the absolute value |dV| of the speeddeviation dV becomes larger, or as the speed deviation gradient |dV|/dtbecomes larger (when the speed deviation dV is in an increasing state),based upon Equation (5):

TBi=KBi 1(Vso)·KBi 2(slope)·KBi 3(accel.)·KBi 4(brake)·KBi 5(μ)·(KBi 6·|dV|+KBi 7 ·|dV|/dt)  (5)

[0136] where, KBi1, as shown in FIG. 11(E), is a coefficient set toincrease from 1 in accordance with acceleration of the vehicle; namely,when the vehicle is being stopped the driver is liable to feelvibrations of the vehicle body caused by braking, and thus thecoefficient KBi1 is set such that the brake control increase amountbecomes smaller: KBi2, as shown in FIG. 11(F), is a coefficient that isset to change in accordance with the road surface gradient; namely, thecoefficient KBi2 is set to become smaller from 1 in accordance withincrease in an upward slope gradient, and to become larger than 1 inaccordance with increase in a downward slope gradient: KBi3, as shown byFIG. 11(G), is a coefficient which is set to decrease from 1 inaccordance with increase in the accelerator opening, and which executescorrection in accordance with the driver's intention: KBi4, as shown byFIG. 11(H), is a coefficient which is set to increase from 1 inaccordance with increase in the brake operation amount, and whichexecutes correction in accordance with the driver's intention: KBi5, asshown in FIG. 11(I), is set so as to decrease from 1 in accordance withdecrease of the road surface μ, and executes correction such that, whenthe road surface μ is low, the braking force is decreased in order toinhibit vehicle behavior from becoming unstable.

[0137] At 516 a new brake control amount BT is set by adding the brakecontrol increase amount TBi determined as described above to a priorbrake control amount BT (t−1). The routine is then exited.

[0138] In the vehicle speed deceleration processing according to thisembodiment, while the engine control is in-progress, first, the enginecontrol amount ET is decreased using the engine decrease amount TEd thatis a decrease gradient; once the engine control has been completed, ifdownshift is possible, first, downshift is executed, and engine brake isapplied; following this, the brake control amount BT is increased usingthe brake control increase amount TBi that is a increase gradient; andthe vehicle speed is decreased to the target creep vehicle speed α.

[0139] Moreover, if the absolute value |dV| of the speed deviation dV islarge, the engine decrease amount TEd becomes large, and the enginecontrol output rapidly becomes zero. In this case, in line with Equation(5), the control delay time DBT is set to become substantially zero.Accordingly, transition from the engine control to downshift or thebrake control is executed continuously.

[0140] In the flow chart of FIG. 10, downshift or increase of the brakecontrol amount is executed immediately following completion of theengine control (processing at 500). However, the downshift or increaseof the brake control amount may be executed after the elapse of apredetermined time period after completion of the engine control.

[0141] Next, the flow of the vehicle speed acceleration processing thatis executed at 312 of FIG. 6 will be explained with reference to FIG.12. It should be noted that this vehicle speed acceleration processingflow corresponds to the vehicle speed acceleration unit of theinvention.

[0142] At 550, it is determined whether automatic brake controls notdirectly related to the driver's brake operation, namely, brake controlexecuted in the brake control of the starting assistance control orbrake control of the VSC control, or the like, is being executed. Thisdetermination is executed in order to make sure that, first, the vehiclespeed acceleration of the brake control is given priority in execution;when this automatic brake control is completed, an engine outputincrease processing of the vehicle speed acceleration processing isexecuted. If automatic brake control is being executed, the routineproceeds to 552, whereas, if automatic brake control is not beingexecuted, the routine proceeds to 556.

[0143] At 552, a brake decrease amount TBd for decreasing braking forcefor each control period is calculated based on Equation (6) in which thelinear sum of the speed deviation dV (dV=α−Vs0) and the speed deviationgradient dV/dt is corrected using the road surface μ and the acceleratoropening:

TBd=KBd 1(μ)·KBd 2(accel.)·(KBd 3 ·dV+KBd 4 ·dV/dt)  (6)

[0144] where, KBd1, as shown in FIG. 13(A), is a coefficient that is setso as to decrease from 1 in accordance with decrease in the road surfaceμ; this coefficient KBd1 executes correction such that the decreaseamount of the braking force becomes smaller in order to minimize theimpact on vehicle behavior when the road surface μ is low: KBd2, asshown in FIG. 13(B), is a coefficient that is set to increase from 1 inaccordance with increase of the accelerator opening; this coefficientKBd2 executes correction such that the decrease amount of the brakingforce becomes larger, because it is necessary to rapidly release brakingforce when the accelerator opening is larger. Further, KBd3 and KBd4 arepre-set proportionality coefficients.

[0145] At 554, the brake decrease amount TBd determined as describedabove is taken as a decrease gradient, and a new brake control amount BTis set which is a value equal to a prior period brake control amount BT(t−1) minus the brake decrease amount TBd. The routine is then exited.

[0146] On the other hand, when it is determined that the automatic brakecontrol is not being executed in at 550, at 556, an engine controlincrease amount TEi for increasing engine output is calculated. Alongwith this, a throttle opening control flag is set that indicates thatcontrol of throttle opening is being executed by the engine control inorder to increase the engine output.

[0147] The engine control increase amount TEi, more specifically, iscalculated based on Equation (7) such that the engine control increaseamount TEi becomes larger as the speed deviation dV becomes larger, oras the speed deviation gradient dV/dt becomes larger (when the speeddeviation dV is in an increasing state), when the vehicle speeddeviation dV is taken as dV=α−Vs0, and the speed deviation gradient istaken as dV/dt:

TEi=KEi 1(Vso)·KEi 2(slope)·KEi 3(accel.)·KEi 4(brake)·KEi 5(μ)·(KEi 6·dV+KEi 7 ·dV/dt)  (7)

[0148] where, KEil, as shown in FIG. 14(A), is a correction coefficientfor vehicle speed change. The correction coefficient value differsdepending on whether the actual direction of travel of the vehicleindicated by the vehicle speed signal, and the direction of travel ofthe vehicle indicated by the shift position of the AT 90 are the samedirection or opposite directions; namely, in the case of the samedirection, when the shift position is the D, 2 or L position, thevehicle speed value is a forward direction value, or alternatively, whenthe shift position is the R position, the vehicle speed value is abackward direction value; on the other hand, in the case of the oppositedirection, when the shift position is the D, 2 or L position, thevehicle speed value is a backward direction value, or alternatively,when the shift position is the R position, the vehicle speed value is aforward direction value.

[0149] The coefficient KEil is set so as to increase from 1 toward anupper limit that is larger than 1, in accordance with increase of theopposite direction vehicle speed from zero. Further, the coefficientKEil is set to increase from a value lower than 1 to an upper limit of1, in accordance with increase of the same direction vehicle speed fromzero toward an extremely low speed range. Namely, when the vehicle VL isprogressing in the opposite direction, the coefficient KEil executescorrection such that the engine control increase amount TEi becomeslarger in order to rapidly change the vehicle direction of travel to thesame direction. Moreover, when the vehicle VL is moving in the samedirection but at an extremely low speed, the coefficient KEil executescorrection such that the engine control increase amount TEi is madesmaller in order to inhibit the driver from feeling a sense of shock dueto rapid acceleration of the vehicle speed.

[0150] Further, in Equation (7) above, KEi2, as shown in FIG. 14(B), isa coefficient which is set so as to increase from 1 in accordance withthe road surface gradient; namely, the coefficient KEi2 is set toincrease from 1 in accordance with increase in an upward slope gradient,and to decrease from 1 in accordance with increase in a downward slopegradient; more specifically, the coefficient executes correction suchthat when the vehicle is on an upward slope the engine control amountTEi becomes larger in order to inhibit the vehicle from slippingbackwards, and when the vehicle is on a downward slope, the enginecontrol amount TEi becomes smaller in order to inhibit the vehicle fromaccelerating suddenly: KEi3, as shown in FIG. 14(C), is a coefficientwhich is set to increase from 1 in accordance with increase of the brakepedal operation amount, and which executes correction in accordance withthe driver's intention: KEi4, as shown in FIG. 14(D), is a coefficientwhich is set to decrease from 1 in accordance with increase of the brakeoperation amount, and which executes correction in accordance with thedriver's intention: KEi5, as shown in FIG. 14(E), is a coefficient whichis set to decrease from 1 in accordance with decrease of the roadsurface μ, and which executes correction by decreasing the enginecontrol increase amount TEi when the road surface μ is low such thatvehicle behavior is inhibited from becoming unstable: further, KEi6 andKEi7 are pre-set proportionality coefficients.

[0151] At 558, the engine control increase amount TEi determined asabove is taken as an increase gradient, and a new brake control amountET is set to be equal to the sum of a prior period engine control amountET (t−1) and the engine control increase amount TCi.

[0152] Next, at 560, an engine output limiter value MAXET thatestablishes a limit for the engine output so as to inhibit, for example,excessive engine output from being generated that is sufficient large toallow the vehicle to go over a concrete stop block in a parking lot, iscalculated based upon Equation (8):

MAXET=R 1(Vso)·R 2(slope)·R 3(accel.)·R 4(brake)·R 5(μ)·MAXET_(init)  (8)

[0153] where, R1 to R5 are coefficients shown respectively in FIGS.14(F) to (J); the respective descriptions and settings of thesecorrection coefficients R1 to R5 correspond to and are the same as thoseof the aforementioned coefficients KEil to KEi5, respectively. As shownin FIG. 7, the engine output is corrected in accordance with the vehiclespeed, the road surface gradient, the accelerator opening, the brakeoperation amount, and the road surface μ. Bearing this correction inmind, a reference value MAXET_(init) is corrected based upon Equation(8), and is set as the limiter value MAXET.

[0154] At 562, the smaller of the engine control amount ET and theengine output limiter value MAXET is selected as a min (ET, MAXET), andthis is set as the engine control amount ET.

[0155] Next, at 564, in the case that the limiter value MAXET has beenset as the engine control amount ET, the routine proceeds to 566. Ifthis is not the case, the routine is terminated.

[0156] At 566, when the vehicle stops or a movement direction of thevehicle is opposite to a direction defined by the shift positionregardless the engine control amount ET reaches the limiter value MAXET,the processing proceeds to 568, otherwise the acceleration processing isterminated.

[0157] At 568 it is not possible to execute vehicle starting with thestarting assistance control (processing 150, namely, processing from 300to 312). Thus, requirements are output for engine output decrease andgeneration of stop maintenance braking force so as to maintain a stoppedstate of the vehicle. Along with this, the starting assistance controlof the vehicle is prohibited.

[0158] As described above, in the vehicle speed acceleration processingof the vehicle speed acceleration unit, if the automatic brake controlis in-progress, first, the brake control amount BT is decreased by thebrake decrease amount TBd that is a decrease gradient; after theautomatic brake control is completed, the engine control amount ET isincreased by the engine control increase amount TEi that is an increasegradient. Then, if the engine control increase amount TEi is too large,the engine control amount ET is increased to the limiter value MAXET,and the vehicle speed is increased to the target creep vehicle speed α.

[0159] It should be noted that in the flow chart of FIG. 12 the engineoutput increase processing (processing at 556) is executed immediatelyafter the brake control is completed (processing at 550). However, adelay time may be provided instead.

[0160] In this way, control is executed such that the actual vehiclespeed is maintained within the range of the target creep vehicle speedα±β, by the vehicle speed deceleration processing at 310 and the vehiclespeed acceleration processing at 312 of FIG. 6.

[0161] Next, the operation flow (refer to FIG. 15) of the bridge control(processing at 314) that is selected when the driver has theacceleration intention or the stop maintenance intention (refer to FIG.6) will be explained. In this bridge control is executed such that theengine control amount and the brake control amount converge on andeventually equal values that accord with the operation amount of thedriver.

[0162] At 600 of FIG. 15 it is determined whether the bridge control ispresently in-progress based on the state of a bridge control in-progressflag (refer to processing at 604). If control is being executed, theroutine proceeds to 606, whereas, if control is not being executed theroutine proceeds to 602.

[0163] At 602, in a state in which the driver has the accelerationintention or the stop maintenance intention, and in which the bridgecontrol is not in-progress, it is determined whether the startingassistance control is in-progress. If it is determined that the startingassistance control is being executed (YES), the routine proceeds to 604in order to shift from the starting assistance control to the bridgecontrol. If it is determined that the starting assistance control is notbeing executed (NO), there is no need to execute the bridge control andthe routine is exited.

[0164] At 604, the bridge control in-progress flag is set, and the flagset at 304 indicating that starting assistance control is in-progress iscleared.

[0165] At 606 it is determined whether W/C pressure has been increasedin order to generate braking force by the automatic brake control. Inparticular, this is applicable to a case where braking force has beengenerated by the automatic brake control on a downward slope. In thisdetermination, it is determined that the W/C pressure has been increasedin this processing if, for example, the W/C pressure increase controlflag has been set at 514 of FIG. 10. In addition, if the result ofprocessing at 606 is YES, the routine proceeds to 608, whereas, if theresult is NO, the routine proceeds to 616.

[0166] At 608, a brake bridge control change amount TB is set so as toprovide a change amount for each control cycle for the brake controlamount, in order to decrease the braking force. In the case that thebrake control amount BT has been set in the automatic brake control,this brake control amount BT is given priority over a brake controlamount BTp that accords with the brake pedal operation amount, and thusbraking force is generated based on the brake control amount BT.However, in the case that the difference between the brake controlamount BT of the automatic brake control and the brake control amountBTp that accords with the brake pedal operation amount is substantial,it is preferable that the brake control amount BT of the automatic brakecontrol is corrected so as to decrease the magnitude of the differenceas rapidly as possible. Accordingly, when the deviation between thebrake control amount BT of the automatic brake control and the brakecontrol amount BTp that accords with the brake pedal operation amount istaken to be dB=BT−BTp, and a gradient of this deviation is taken to bedB/dt, the brake bridge control change amount TB is set so as toincrease as the braking force deviation dB increases, and as thedeviation gradient dB/dt increases (when the braking force deviation isin an increasing state). More particularly, the brake bridge controlchange amount TB is calculated based on Equation (9)

TB=M 1(μ)·M 2(accel.)·(N 1·dB+N 2·dB/dt)  (9)

[0167] where, M1, as shown in FIG. 16(A) is a coefficient which is setto decrease from 1 in accordance with decrease of the road surface μ,and which executes correction so as to decrease the decrease amount ofthe braking force in order to minimize instability in the vehiclebehavior when the road surface μ is low: M2, as shown in FIG. 16(B), isa coefficient which is set to increase from 1 in accordance withincrease in the accelerator opening, and which executes correction so asto increase the decrease amount of the braking force since it isnecessary to release the braking force rapidly when the accelerationopening degree is large: further, N1 and N2 are pre-set proportionalitycoefficients.

[0168] At 610, the brake control amount BT of the automatic brakecontrol is renewed using a value that is equal to the brake controlamount BT of the present control minus the aforementioned brake bridgecontrol change amount TB.

[0169] At 612, it is determined whether the renewed brake control amountBT has become equal to the brake control amount BTp that accords withthe brake pedal operation amount. If the result is YES, at 614, the W/Cpressure increase flag is reset, and the brake bridge control isterminated. If the result is NO, the routine proceeds to 616.

[0170] At 616 it is determined whether control of the throttle openingis being executed by the engine control that is in-progress in order toincrease the engine output. In particular, this applies to a case whenengine output is being raised by the engine control on an upward slope.In this determination it is determined that the throttle opening isbeing controlled based upon the engine control in this processing if,for example, the throttle opening control flag is set at 556 of FIG. 12.In addition, if the result of processing at 616 is YES, the routineproceeds to 618, whereas, if the result is NO, the bridge controlroutine is exited.

[0171] At 618, the engine bridge control change amount TE that providesthe change amount for the engine control amount is set such that theengine output is decreased for each period. In the case that the enginecontrol amount ET of the engine control is set, this engine controlamount ET is given priority over an engine control amount ETp thataccords with the accelerator pedal operation amount, and thus the engineoutput is generated based on the engine control amount ET. However, inthe case that the difference between the engine control amount ET of theengine control and the engine control amount ETp that accords with theaccelerator pedal operation amount is substantial, it is preferable thatthe engine control amount ET of the engine control is corrected so as todecrease the magnitude of the difference as rapidly as possible.Accordingly, when the deviation between the engine control amount ET ofthe engine control and the engine control amount ETp that accords withthe accelerator pedal operation amount is taken to be dE=ET−ETp, and agradient of this difference is taken to be dE/dt, the engine bridgecontrol change amount TE is set so as to increase as the engine outputdeviation dE increases, and as the deviation gradient dE/dt increases(when the engine output deviation is in an increasing state). Moreparticularly, the engine bridge control change amount TE is calculatedbased on Equation (10):

TE=M 3(μ)·M 4(brake)·(N 3·dE+N 4·dE/dt)  (10)

[0172] where, M3, as shown in FIG. 16(C), is a coefficient that is setso as to decrease from 1 in accordance with decrease of the road surfaceμ, and which executes correction so as to reduce the reduction amount ofthe engine output in order to minimize instability in vehicle behaviorwhen the road surface μ is low: M4, as shown in FIG. 16(D) is acoefficient which is set to increase from 1 in accordance with increasein the brake pedal operation amount, and which executes correction so asto increase the decrease amount of the braking force since it isnecessary to decrease the engine output rapidly when the brake operationamount is large: further, N3 and N4 are pre-set proportionalitycoefficients.

[0173] At 620, the engine control amount ET that provides a targetengine output is renewed with a value equal to the engine control amountET of the present control minus the engine bridge control change amountTE.

[0174] At 622, it is determined whether the renewed engine controlamount ET has become equal to the engine output ETp that accords withthe accelerator pedal operation amount. If the result is YES, at 624,the throttle opening control flag is reset and the engine bridge controlis terminated. If the result is NO, the bridge control routine isexited.

[0175] In this way, the brake control amount or the engine controlamount set in the bridge control routine, namely, the respective brakecontrol amount BT or the engine output ET of the automatic control, isgradually changed (each control cycle) so as to respectively equal thebrake control amount BTp or the engine output ETp that accord withrespective pedal operations, by using the brake bridge control changeamount TB or the engine bridge control change amount TE as changegradients.

[0176] Following this, the processing of the starting assistance controlof processing at 150 (refer to FIG. 3) is completed.

[0177] Next, a procedure of brake control adjustment of processing at160 will be explained with reference to the flow chart of FIG. 17.

[0178] At 700, the braking force requirement for the VSC control and theTCS control set at 140 is compared with the braking force requirement ofthe starting assistance control set at 150, and the larger of thesevalues is selected.

[0179] Next, at 702, the selected braking force requirement is set as abrake command value for each wheel.

[0180]FIG. 18 is a flow chart of output processing for the motor-drivenPKB 3 that is executed at 190.

[0181] At 800, it is determined whether the present operation state ofmotor-driven PKB 3 is a cancelled state or not. If the motor-driven PKB3 is in the cancelled state the routine proceeds to 802, whereas, if theresult is NO, namely, if it is in a locked state, the routine proceedsto 812.

[0182] At 802, it is determined whether the vehicle stop maintenancestart switch 56 has been switched to ON, namely, whether, a motor-drivenPKB 3 lock requirement has been generated. If the result is YES, theroutine proceeds to 808 and drive conditions for a locking operation areset. If the result is NO, the routine proceeds to 804.

[0183] At 804, if the vehicle stop maintenance condition, for example,whether the brake pedal has been depressed for four seconds or moresince stopping of the vehicle VL, is satisfied, the routine proceeds to808; however, if not satisfied, the routine proceeds to 806.

[0184] At 806, if the shift position is a position that makes driveinoperable (i.e., the P or N positions), the routine proceeds to 808;however, if the position makes drive operable (i.e., the D, 2 or Lpositions), the routine proceeds to 822, and the drive conditions forstopping drive of the motor-driven PKB 3 are set.

[0185] At 808, the motor drive conditions for locking the motor-drivenPKB 3 are set such that drive is executed at a 100% duty ratio with anormal rotation direction.

[0186] At 810, it is determined whether the locking operation of themotor-driven PKB 3 is completed, namely, the locking operation iscompleted when rotation stops of the motor that is being driven so as toreach a locked state. Further, as the method for determining whether themotor has stopped, it is possible to utilize the actual rotation speedof the motor, or alternatively, it is possible to use a motor currentthat corresponds to a locked current. If this determination result isYES, the routine proceeds to 822 and the motor drive conditions are setsuch that drive is executed with a 0% duty ratio and a normal rotationdirection; in other words, the drive conditions are set so that themotor is not driven. Following this, the routine proceeds to 824. On theother hand, if the result is NO, the routine proceeds directly to 824,and in this processing, the actuator (the motor) is driven in accordancewith the set drive conditions.

[0187] Meanwhile, when the motor-driven PKB 3 is in a locked state, at812, it is determined whether the switch operation for the releaserequirement of the motor-driven PKB 3 (for example, switching thevehicle stop maintenance start switch 56 to OFF) has been executed. Ifthe result is YES, the routine proceeds to 818 and the motor driveconditions for the cancel operation are set. If the result is NO, theroutine proceeds to 814.

[0188] At 814, when the locking operation of the motor-driven PKB 3 isbeing executed due to the vehicle stop maintenance start condition beingsatisfied, if the condition, for example, “accelerator pedal operationpresent”, is satisfied, the routine proceeds to 818. If such a conditionis not satisfied, the routine proceeds to 816.

[0189] At 816, when the locking operation of the motor-driven PKB 3 isbeing executed due to satisfaction of the drive inoperable positioncondition of the shift position, if the shift position is shifted to adrive operable position (i.e., the D, 2 or L positions), the routineproceeds to 818. If the shift position is the drive inoperable position(i.e., the P or N positions) the routine proceeds to 822.

[0190] At 818, the motor drive conditions for releasing the motor-drivenPKB 3 are set such that drive is executed at a 100% duty ratio with areverse rotation direction.

[0191] At 820, when a rotation amount of the motor of the motor-drivenPKB 3 reaches a predetermined amount (e.g., a position that is returnedby 15 mm from the locked position), the release operation is completed.If this condition is satisfied, the routine proceeds to 822, and themotor drive conditions are set such that drive is not executed; however,if the conditions are not satisfied, the routine proceeds to 824, andthe motor is driven in accordance with the set drive conditions.

[0192] As described above, according to the first embodiment, in thecase that the driver has neither one of the acceleration intention orthe stop maintenance intention, the target creep vehicle speed α is set,and the vehicle speed deceleration processing or the vehicle speedacceleration processing is executed. Accordingly, it is possible tocontrol the actual vehicle speed such that it becomes the target creepvehicle speed α or a value within a fixed range in the vicinity of thetarget creep vehicle speed α.

[0193] The target creep vehicle speed α is set in accordance with thedriver's driving operations (the accelerator opening, the brakeoperation amount, etc.), the driving state (the direction of travel ofthe vehicle, distance from obstacles, etc.), and the road surfaceconditions (the road surface gradient). Thus, it is possible to set thetarget value in accordance with circumstances. Moreover, in the casethat the deviation of the actual vehicle speed and the target creepvehicle speed α is large, the new target value is set to a value thatgradually changes from the actual vehicle speed based on a value that isin accordance with the deviation amount. Accordingly, it is possible toset the target value in accordance with the actual driving conditions.

[0194] In the vehicle speed deceleration processing, after the engineoutput is decreased, downshift and the brake control amount increaseprocessing is executed, and thus it is possible to smoothly decrease thevehicle speed to the target value.

[0195] In the vehicle speed acceleration processing, after the brakingforce is cancelled, the engine output is increased up to the limitvalue, and thus it is possible to smoothly increase the vehicle speed tothe target value without generating excessive engine output.

[0196] In the vehicle speed deceleration processing and the vehiclespeed acceleration processing, the increase amount and the decreaseamount of the braking force, and the increase amount and the decreaseamount of the engine output are corrected in accordance with thedriver's driving operations (the accelerator opening, the brakeoperation amount, etc.), the driving state (the vehicle speed, thedirection of travel of the vehicle, etc.), and the road surfaceconditions (the road surface μ the road surface gradient, etc.).Accordingly, it is possible to execute vehicle speed control that is inaccordance with driving operations and which does not impact on vehiclebehavior.

[0197] Thus, on sloping roads, such as upward sloping and downwardsloping roads, it is possible to make the vehicle VL drive at low speedin the direction in which the vehicle VL is facing. Therefore, it ispossible to execute starting of the vehicle VL more easily.

[0198] Moreover, when the vehicle speed control is completed in whichthe target creep vehicle speed α is set to the target value inaccordance with operations that are based on the driver's accelerationintention and stop maintenance intention, the brake control amount andthe engine control amount are changed by the bridge control such thatthe braking force and the engine output are in accordance with thedriver's respective operations of the accelerator and brake pedals.Thus, it is possible to smoothly execute the acceleration operation andstop maintenance operation of the vehicle VL.

[0199] (Second Embodiment)

[0200] Next, a creep drive control device according to the secondembodiment of the invention will be explained. The second embodiment isconfigured to have exactly the same structure and operation as the firstembodiment, with the exception of the details of the processing of thebrake control adjustment of processing at 160 (refer to FIG. 3).Hereinafter, an explanation will only be given concerning this point ofdifference. A description of the other structure, the operation, and thedrawings of the second embodiment will be omitted.

[0201]FIG. 19 shows a flow chart of brake control adjustment accordingto the second embodiment.

[0202] At 700, as with the first embodiment, the braking forcerequirement value of the VSC control and TCS control and the brakingforce requirement value of the starting assistance control set at 150are compared, and the larger value is selected.

[0203] At 704, if the braking force requirement value selected at 700 isthe braking force requirement value of the starting assistance control,the routine proceeds to 710. However, if the other braking forcerequirement value is selected, the routine proceeds to 706.

[0204] At 706, the braking force of the four wheels is set in accordancewith the braking force requirement value of the VSC control and the TCScontrol, and then at 708, a control time timer ConT of the startingassistance control is cleared.

[0205] At 710, the control time timer ConT is increased by an incrementof 1, and next, at 712, it is determined whether the control time timerConT has exceeded a predetermined time T1.

[0206] If the result of processing at 712 is NO, at 714, a controlpressure is set such that braking forcing is only applied to two of thediagonally connected wheels (the wheels 4FR and 4RL).

[0207] If the result of processing at 712 is YES, the routine proceedsto 716, and application of the braking force is switched to the othertwo diagonally connected wheels (the wheels 4FR and 4RL).

[0208] In the determination of processing at 718, it is determinedwhether the control time timer ContT equals a predetermined time T2 thatcorresponds to double the predetermined time T1 (T2=2×T1). In addition,if the predetermined time T2 has elapsed, the control time timer ConT iscleared at 720, and after this, next time, the processing switches toapplying braking force to the other two diagonally connected wheels. Ifthe predetermined time T2 has not elapsed, the routine is directlyexited.

[0209] In this way, according to the second embodiment, the brakingforce of the vehicle speed deceleration processing executed during thestarting assistance control is switched each time the predetermined timeT1 elapses, from being applied to one set of the two diagonallyconnected wheels to the other set of the two diagonally connectedwheels. Accordingly, it is possible to decrease the energizing time foreach of the actuators of the control valves, and so on, which isbeneficial from the point of view of the maintenance lifetime of thehydraulic brake device 2.

[0210] (Third Embodiment)

[0211] Next, a creep drive control device of a third embodimentaccording to the invention will be explained. This third embodiment,like the first and second embodiments, is provided with the samestructural elements as shown in FIG. 1 of the entire structure and isalso provided with the hydraulic brake device (FIG. 2). Accordingly, anexplanation of these structural elements will be omitted here.

[0212]FIG. 20 shows a main flow chart of a creep drive control deviceaccording to the third embodiment. This flow chart differs from that ofthe first and second embodiments with respect to the details of theprocessing at 165 and 192, in which the application method for thebraking force of the starting assistance control is different. However,all the other processing are the same as those shown in FIG. 3;accordingly, the same reference characters are used to denote sectionsthat are the same, and an explanation is omitted here.

[0213] The procedure of brake control adjustment of processing 165, willbe explained with reference to the flow chart of FIG. 21.

[0214] At 700, as with the first and second embodiments, the brakingforce requirement value of the VSC control and the TCS control and thebraking force requirement value of the starting assistance control setat 150 are compared, and the larger value is selected. Moreover, if anyother braking force requirement values are output from other automaticcontrol ECUs, such as the congestion adaptive cruise control ECU (notshown), these values may also be incorporated within the comparison ofthis processing.

[0215] At 704 to 708, 710 and 712, the same processing as in therespective processing of the second embodiment is executed, and thus anexplanation will be omitted here.

[0216] At 715, during the period when the control time timer ConT of thestarting assistance control is less than or equal to the predeterminedtime T1, the braking force is only applied by the hydraulic brakingdevice 2 to the rear wheels 4RL and 4RR.

[0217] On the other hand, when the control time timer ConT exceeds thepredetermined time T1, at 717, the brake pressure of the motor-drivenPKB 3 is set in order to switch generation of the braking force for therear wheels from the hydraulic brake device 2 to the motor-driven PKB 3.

[0218] As even more time elapses and the control time timer ConT exceedsthe predetermined time T2 (processing at 718), the control time timerConT is cleared as in the aforementioned second embodiment (processingat 720). As a result, from next time, the braking force of the rearwheels 4RR and 4RL switches to being generated by the hydraulic brakedevice 2.

[0219] Moreover, according to the third embodiment, the outputprocessing for the motor-driven PKB 3 at 195 is different to that of thefirst and second embodiments. FIGS. 22 and 23 are flow charts showingthe procedure for this output processing.

[0220] With the exception of processing at 807, 800 to 824 are the sameas those in the first and second embodiments above, and thus anexplanation will be omitted here.

[0221] At 807, if the shift position is a position that makes driveinoperable (i.e., the P or the N position), the routine proceeds to 808,as is the case with the previous embodiments. However, the routinediffers from those of the previous embodiments with respect to the factthat if the shift position is a position that makes drive operable(i.e., the D, 2 or L position), the routine proceeds to 826 (refer toFIG. 23) instead of processing at 822.

[0222] In other words, at 826 it is determined whether there is acontrol requirement for the motor-driven PKB 3 from the brake controladjustment, namely, it is determined whether the braking force for themotor-driven PKB 3 is set at 165, or more specifically, at 717. If theresult is YES, the routine proceeds to 828, whereas, if the result isNO, the routine proceeds to 836.

[0223] At 828, the braking force requirement value is converted into astroke value based on the relationship of the braking force requirementvalue (e.g., in MPa units), a stroke of the brake wire 31R and 31L ofthe motor-driven PKB 3, and the braking force (FIG. 24). It should benoted that, in FIG. 24, the point at which braking force first begins tobe generated is designated as a wire stroke of zero mm.

[0224] Next, at 830, the present wire stroke and the required strokevalue are compared, and if the required stroke value is large theroutine proceeds to 832, whereas, if it is small, the routine proceedsto 834.

[0225] The point at which braking force first beings to be generated canbe distinguished based on the magnitude of the current of the motor ofthe motor-driven PKB 3, since it is the point at which small current, ata time when there is no load, changes extensively. Accordingly, bydetecting and memorizing this point in advance for prior motor-drivenPKB 3 operations, it is possible to compare a value that is the sum ofthe stored value and the required stroke value obtained at 828, with thepresent wire stroke (the present position).

[0226] At 832, the motor drive conditions are set such that drive isexecuted at a 30% duty ratio with a normal rotation direction, so as toincrease the braking force of the motor-driven PKB 3.

[0227] At 834, the motor drive conditions are set such that drive isexecuted at a 30% duty ratio with a reverse rotation direction, so as todecrease the braking force of the motor-driven PKB 3.

[0228] On the other hand, when there is no braking force requirement forthe motor-driven PKB 3 from the brake adjustment, at 836, it isdetermined whether there is any history of braking force requirementsfrom the brake adjustment.

[0229] If there is a history, namely, if there has been a movement froma state in which there was a braking force requirement to a state inwhich there was no braking force requirement, it is necessary to releasethe presently generated braking force of the motor-driven PKB 3. Thus,the routine proceeds to 838. In the case that there is no history, theroutine proceeds to 842 and the motor drive conditions are set such thatthe motor is not driven.

[0230] At 838, the motor drive conditions are set such that drive isexecuted at a 100% duty ratio with a reverse rotation direction, so asto release the braking force of the motor-driven PKB 3.

[0231] At 840, it is determined whether the brake wire 31R or 31L hasbeen returned by the wire stroke amount that was generated at 832 sincethe drive of the motor-driven PKB 3 in the reverse direction started.This determination is based upon whether the rotation amount of themotor has exceeded a total revolution amount. If the result is YES, theroutine proceeds to 842 and the motor drive conditions are set such thatthe motor is not driven; whereas, if the result is NO, the routineproceeds to 824 and drive in the reverse direction of the actuator (themotor) is continued.

[0232] As described above, according to the third embodiment,application of braking force to the two rear wheels in the startingassistance control is conducted such that execution is switched betweenthe hydraulic brake device 2 and the motor-driven PKB 3 every time thepredetermined time elapses. In other words, it is possible to inhibitdamage resulting from heat discharge of the hydraulic brake device 2since the burden of generating braking force during the vehicle speeddeceleration processing when causing the vehicle speed to equal thetarget creep vehicle speed α is shared by the motor-driven PKB 3.

[0233] (Other Embodiments)

[0234] According to the aforementioned embodiments, the hydraulic brakedevice 2 shown in FIG. 2 was employed as an example of the first brakeunit that applies braking force to each wheel. However, in addition tothis configuration, it is possible to increase the pressure applied tothe master cylinder using not only application by normal depression ofthe brake pedal, but also another controlled hydraulic mechanism thatapplies pressure independently of the brake pedal force. In other words,it is possible to use a so-called hydro-booster that makes it possibleto increase the pressure of the master cylinder even when there is nobrake pedal operation.

[0235] Moreover, as the first brake unit, a motor-driven brake devicemay be adopted in which an electric motor is provided in each wheel, andbraking force is generated by directly pressing the brake calipersagainst the brake disk using drive of the electric motor, regardless ofhydraulic pressure.

[0236] In the above examples, the described configurations function asthe first brake unit in which the first braking force is generated basedupon the actuating signal, and in which the braking force is cancelled(i.e., braking force equals zero) when the actuating signal iscancelled. Accordingly, it is possible to generate braking force in ahighly responsive manner.

[0237] While the above description is of the preferred embodiments ofthe present invention, it should be appreciated that the invention maybe modified, altered, or varied without deviating from the scope andfair meaning of the following claims.

What is claimed is:
 1. A creep drive control device that executes, whena driver of a vehicle does not have either one of an intention toaccelerate the vehicle and an intention to maintain stopping of thevehicle, at least one of adjustment of a braking force applied to thevehicle and adjustment of a driving force of the vehicle so as toexecute control such that a vehicle speed becomes a value within a fixedrange.
 2. A creep drive control device comprising: an engine outputcontrol unit that controls an engine output in accordance with an enginecontrol amount; a braking force control unit that controls a brakingforce applied to each wheel in accordance with a brake control amount;an acceleration intention determination unit that determines whether adriver has an acceleration intention; a stop maintenance intentiondetermination unit that determines whether the driver has a stopmaintenance intention; a target creep vehicle speed setting unit thatsets a target creep vehicle speed; a vehicle speed acceleration unitthat increases a vehicle speed by at least one of increasing the engineoutput and decreasing the braking force; a vehicle speed decelerationunit that decreases a vehicle speed by at least one of decreasing theengine output and increasing the braking force; a starting assistancecontrol unit which, when respective results of determinations by theacceleration intention determination unit and the stop maintenanceintention determination unit are negative, operates using a creepdriving mode in which the vehicle speed acceleration unit is operatedwhen the vehicle speed is less than a first target vehicle speed that issmaller than the target creep vehicle speed by a predetermined amount,and in which the vehicle speed deceleration unit is operated when thevehicle speed is larger than a second target vehicle speed that islarger than the target creep vehicle speed by a predetermined amount. 3.The creep drive control device according to claim 2, wherein theacceleration intention determination unit determines that the driver hasthe acceleration intention when a shift position of an automatictransmission is set to a drive operable position by the driver, and whenthe acceleration intention determination unit detects at least one of anaccelerator opening being equal to a predetermined amount, the vehiclespeed being equal to or above a predetermined value, and the drive ofthe vehicle being controlled by an automatic driving control other thanthe control executed by the starting assistance control unit.
 4. Thecreep drive control device according to claim 2, wherein the stopmaintenance determination unit determines that the driver has the stopmaintenance intention when the stop maintenance determination unitdetects at least one of setting of a shift position of an automatictransmission to a drive inoperable position by the driver, execution ofa brake operation that generates braking force capable of causing stopmaintenance of the vehicle, and execution of an automatic stop controlthat automatically stops the vehicle.
 5. The creep drive control deviceaccording to claim 2, wherein the target creep vehicle speed settingunit sets the target creep vehicle speed by correcting a pre-setreference creep vehicle speed in accordance with at least one of adriving state of the vehicle, a road surface condition, and a drivingoperation of the driver.
 6. The creep drive control device according toclaim 5, wherein the target creep vehicle speed setting unit executescorrection such that the target creep vehicle speed becomes larger as anaccelerator opening becomes larger.
 7. The creep drive control deviceaccording to claim 5, wherein the target creep vehicle speed settingunit executes correction such that the target creep vehicle speedbecomes smaller as a brake operation amount becomes larger.
 8. The creepdrive control device according to claim 5, wherein the target creepvehicle speed setting unit executes correction such that the targetcreep vehicle speed when the vehicle is moving in a backward directionis smaller than the target creep vehicle speed when the vehicle ismoving in a forward direction.
 9. The creep drive control deviceaccording to claim 5, wherein the target creep vehicle speed settingunit executes correction such that the target creep vehicle speedbecomes smaller as a distance becomes smaller between the vehicle and anobstacle in a forward direction of the vehicle.
 10. The creep drivecontrol device according to claim 5, wherein the target creep vehiclespeed setting unit executes correction such that the target creepvehicle speed becomes larger on a road with a downward gradient, and thetarget creep vehicle speed becomes smaller on a road with an upwardgradient.
 11. The creep drive control device according to claim 5,wherein the target creep vehicle speed setting unit executes correctionsuch that the target creep vehicle speed becomes larger in accordancewith a length of continuation of a state in which the braking forcegenerated by the braking force control unit is equal to or above apredetermined value.
 12. The creep drive control device according toclaim 2, wherein the target creep vehicle speed setting unit sets, whena deviation between a present vehicle speed and the target creep vehiclespeed is larger than a predetermined value, a new target creep vehiclespeed that is the sum of the present vehicle speed and a value thataccords with the deviation.
 13. The creep drive control device accordingto claim 2, wherein the vehicle speed acceleration unit increases thevehicle speed by increasing the engine output after decreasing thebraking force.
 14. The creep drive control device according to claim 2,wherein the vehicle speed deceleration unit decreases the vehicle speedby increasing the braking force after decreasing the engine output. 15.The creep drive control device according to claim 14, wherein thevehicle speed deceleration unit decreases the vehicle speed bydecreasing the engine output, and following this, increasing a gearratio of a transmission.
 16. The creep drive control device according toclaim 2, wherein the vehicle speed acceleration unit increases thevehicle speed by at least one of setting a second engine control amountwith which the engine output is controlled by the engine output controlunit as the sum of the engine control amount and an engine controlincrease amount, and setting a second brake control amount with whichthe braking force is controlled by the braking force control unit as thebrake control amount minus a brake decrease amount.
 17. The creep drivecontrol device according to claim 2, wherein the vehicle speeddeceleration unit decreases the vehicle speed by at least one of settinga second brake control amount with which the braking force is controlledby the braking force control unit as the sum of the brake control amountand a brake control increase amount, and setting a second engine controlamount with which the engine output is controlled by the engine outputcontrol unit as the engine control amount minus an engine decreaseamount.
 18. The creep drive control device according to claim 16,wherein the engine control increase amount and the brake controlincrease amount are respectively set in accordance with a deviationbetween the vehicle speed and the target creep vehicle speed.
 19. Thecreep drive control device according to claim 18, wherein the enginecontrol increase amount and the brake control increase amount arerespectively corrected in accordance with at least one of a drivingstate of the vehicle, a road surface condition, and a driving operationof the driver.
 20. The creep drive control device according to claim 16,wherein the brake decrease amount is set by correcting an amount thataccords with a deviation between the braking force that accords with thebrake control amount and a braking force that accords with a brakeoperation amount, using at least one of an accelerator opening and aroad surface coefficient of friction.
 21. The creep drive control deviceaccording to claim 17, wherein the engine decrease amount is set bycorrecting an amount that accords with a deviation between the vehiclespeed and the target creep vehicle speed, using at least one of a brakeoperation amount and a road surface coefficient of friction.
 22. Thecreep drive control device according to claim 2, wherein the vehiclespeed acceleration unit limits the engine control amount such that theengine control amount is equal to or less than an upper limit value. 23.The creep drive control device according to claim 22, wherein thevehicle speed acceleration unit executes correction of the upper limitvalue in accordance with at least one of a driving state of the vehicle,a road surface condition, and a driving operation of the driver.
 24. Thecreep drive control device according to claim 16, wherein the vehiclespeed acceleration device executes correction such that the enginecontrol increase amount becomes smaller in either one of a case that thevehicle speed is a value proximate to zero, and a case that a gradientof a road surface is a downward gradient.
 25. The creep drive controldevice according to claim 16, wherein the vehicle speed accelerationunit executes correction such that the engine control increase amountbecomes smaller in accordance with any one of an accelerator openingbecoming smaller, a brake operation amount becoming larger, and a roadsurface coefficient of friction becomes smaller.
 26. The creep controldevice according to claim 22, wherein, when the engine control amount islimited to being equal to or less than the upper limit value, thevehicle speed acceleration unit suspends engine output control when thevehicle is either one of stationary and moving in a direction oppositeto a direction of travel of the vehicle, and along with this, thestarting assistance control unit causes the braking force control unitto generate a stop maintenance braking force for stop maintenance of thevehicle.
 27. The creep drive control device according to claim 17,wherein the vehicle speed deceleration unit executes correction suchthat the brake control increase amount becomes larger in accordance withany one of an accelerator opening becoming smaller, a brake operationamount becoming larger, and a road surface coefficient of frictionbecoming larger.
 28. The creep drive control device according to claim17, wherein the vehicle speed deceleration unit executes correction suchthat the brake control increase amount becomes larger when a gradient ofa road surface is a downward gradient.
 29. The creep drive controldevice according to claim 16, wherein, when the vehicle speed increasesfollowing decrease of the engine output by the vehicle speeddeceleration unit, the braking force control unit switches the wheel towhich the braking force is applied during a period in which the brakingforce is applied.
 30. The creep drive control device according to claim16, wherein the braking force control device is provided with a firstbraking unit that applies braking force to each wheel, and a secondbraking unit which applies braking force to each wheel independently ofthe first brake unit, and when the vehicle speed increases followingdecrease of the engine output by the vehicle speed deceleration unit,the braking force control unit switches between generation of thebraking force by the first braking unit and generation of the brakingforce by the second braking unit, during a period in which the brakingforce is applied.
 31. The creep drive control device according to claim2, wherein the starting assistance control unit causes the enginecontrol amount to change such that the engine control amount agrees withan amount that accords with an accelerator pedal operation amount of thedriver, when the creep driving mode is completed.
 32. The creep drivecontrol device according to claim 2, wherein the starting assistancecontrol unit causes the brake control amount to change such that thebrake control amount agrees with an amount that accords with a brakepedal operation amount of the driver, when the creep driving mode iscompleted.